How do you write a magic file test pattern to match the end of a file?

Question

I am beginning to wonder if this is even possible as multiple searches on SO, Google, Bing and linuxquestions.org have turned up nothing.

I am interested in extending the magic patterns located in /usr/share/magic (used by the file(1) utility) to recognize files based on data at or near the end of the file. I have been able to do this for the beginning of a file, as well as for arbitrary offsets into the file from the beginning.

The man page does a pretty good job of illustrating some standard usage cases; unfortunately, it does not seem like there is a way to index from the end as opposed to the beginning. The only workaround I could come up with was to adopt a scripted approach using tac and/or lreverse but feel these may be unfriendly to binary data.

Also, I wanted to avoid any other scripted processing - I feel like this should be doable with the right file magic. Any ideas?